(1) Field of the Invention
This invention is a composition of matter that may be used to prepare the internal metal surfaces of an internal combustion engine to accept a coating of fluoropolymer lubricant. The composition of this invention facilitates the bonding of a fluoropolymer to the internal surfaces of an internal combustion engine by neutralizing and removing zinc dialkyldithiophosphate from the metal surfaces of an internal combustion engine prior to flouoropolymer bonding. This invention is also a method for using the composition to pretreat the internal metal surfaces of an internal combustion engine to accept a fluoropolymer.
(2) Description of the Art
Internal combustion engines are relatively inefficient. One area where energy is lost is through friction between the engine pistons and cylinder walls. Furthermore, the friction causes undesirable piston and cylinder wear. Oil lubricants reduce the energy lost through piston/cylinder friction and they reduce piston and friction wear. It has been discovered that a coating of a fluoropolymer applied to the internal metal surfaces of an engine's cylinders and pistons further reduces piston/cylinder friction and wear thereby improving engine efficiency and longevity.
The lubricating properties of fluoropolymers are well known. Most consumers are familiar with fluoropolymers used as anti-stick agents in pots and pans. U.S. Pat. No. 4,983,677 and an article by D. E. Priester et al. New Processing Additives For Polyolefins Minimize Formulation Interactions, ANTEC 92 2024-27 (1992), describe methods for improving the efficiency of polymer extrusion, blow molding, and other polymer processes by coating the metal processing parts with a fluoropolymer. The fluoropolymer is added to a polymer composition from which the fluoropolymer deposits on the metal surfaces of the extruder or the mold.
Treating an internal combustion engine with a fluoropolymer has a similar effect. The fluoropolymer adheres to the surfaces of the cylinder and the piston. The adhered fluoropolymer acts as a lubricant and it reduces the friction caused by the movement of the piston in the engine cylinder. This, in turn, improves engine efficiency and it reduces engine wear.
The ability of a fluoropolymer to adhere to a metal surface is not absolute. Many chemicals and compounds actually inhibit the ability of a fluoropolymer to adhere to a metal surface. U.S. Pat. No. 5,064,594 describes talc and silica polymer melt additives as having a detrimental effect on the ability of the fluoropolymer to adhere to metal parts due to their abrasive nature. The article by D. E. Priester, cited above, discloses that polyolefin additives such as antiblock agents, pigments, and acid scavengers can have a detrimental effect on the ability of a fluoropolymer to coat to a metal surface. And U.S. Pat. No. 4,704,423 discloses that metal salts of higher fatty acids have the potential to reduce the effectiveness of a fluoropolymer as a lubricant processing aid.
Fatty acid derivatives and compounds such as calcium stearate or zinc stearate are materials that are sometimes used in motor oil additives as, for example, acid scavengers. Most premium motor oils include an additive, zinc dialkyldithiophosphate, that coats the piston and cylinder metal parts and that inhibits the ability of a fluoropolymers to bind to the metal piston and cylinder walls. As a result, the internal metal surfaces of an internal combustion engine that are coated with zinc dialkyldithiophosphate cannot easily accept a fluoropolymer.